The present invention relates to intervertebral support systems, and to systems for promoting intervertebral bone fusion.
A variety of support assemblies currently exist which may be surgically implanted into a patient""s intervertebral space so as to provide support between two (or more) adjacent vertebrae. Surgical implantation of such systems is typically used to provide support along the spinal column in cases where a portion of the patient""s intervertebral anatomy has become diseased or destroyed. In addition, such support systems are also commonly used following a diskectomy, wherein the patient""s intervertebral disk is surgically removed.
A drawback of these existing support systems is that they tend to be somewhat large and bulky, especially when these systems operate to provide support across a large portion of the patient""s vertebral region. Being large and bulky, surgical implantation of these systems into a patient""s vertebral region often creates a substantial amount of trauma to the patient.
Moreover, the installment of such large, bulky support systems into a patient""s intervertebral space typically also requires a large amount of tissue to first be removed from the patient""s intervertebral space so as to make way for the device.
Most commonly, existing support systems typically operate by inhibiting (normal) movement between the adjacent vertebrae, thereby holding these vertebrae at fixed positions relative to one another, with the mechanical body of the supporting structure providing the needed support along the patient""s spinal column. Such supporting systems are typically made of stainless steel or titanium, and are designed to permanently remain within the patient""s body.
The present invention provides a novel system of intervertebral support using a pair of bone allografts and a pair of facet screws.
An advantage of the present system is that, by inhibiting motion between two adjacent vertebrae, it facilitates natural bone fusion between these vertebrae. An advantage of the present invention""s use of bone allografts (positioned between the vertebrae) is that these allografts will eventually be resorbed into the patient""s body as bone growth between the immobilized vertebrae progresses. In contrast, existing mechanical (e.g.: metallic) intervertebral support structures simply remain as large permanent foreign structures within the patient""s body. In preferred aspects, motion between the two adjacent vertebrae is specifically inhibited by the facet screws, as will be explained.
The present system advantageously provides intervertebral support at three locations in particular, with these three locations together forming a triangle. Specifically, each of the facet screws provides support at the facet joints (which are disposed at two symmetrically spaced apart locations at the posterior or rear of the vertebral column). The bone allografts are preferably positioned to provide support at an anterior (i.e. front), central location in the vertebral column. An advantage of the present three point (i.e.: triangular) support system is that support is provided in three perpendicular directions, (thereby providing support with respect to forward-backward bending, side-to-side bending and torsion of the spine). Furthermore, the present three point (i.e.: triangular) support system provides support at three separate locations which are spaced apart over a relatively large section of the patient""s spinal column, providing enhanced stability. Specifically, the three sides of the present support triangle correspond to the locations of the two facet joints and the inter vertebral disc.
An important advantage of the present system is that it can be assembled in a minimally invasive percutaneous (preferably cannulated) surgical approach. In contrast, existing systems which provide support across a wide area of the patient""s vertebrae typically comprise a single large integrated structure which substantially fills the patient""s intervertebral space, and which is typically installed during a major invasive open surgical procedure. A further advantage of the present assembly is that since it comprises four separate components, (two bone allografts and two facet screws), these four components can be installed sequentially, with each of the components being installed through a cannula. In contrast, existing intervertebral support systems typically comprise a single large assembly which cannot be installed through a cannula.
In preferred aspects, the two bone allografts are positioned at an angle to one another. An advantage of having the bone allografts disposed angled to one another is that they provide support in perpendicular directions (i.e.: along two axes which are angled to one another). Specifically, in a preferred case using long, narrow shaped bone allografts, the bone allografts are preferably positioned with their long central longitudinal axes disposed at an angle to one another.
Since the present pair of bone allografts are positioned at an angle to one another, tall, narrow bone allografts can be used. Advantages of using a tall, narrow bone allograft include its fabrication requiring less bone material than would be used in conventionally manufactured allografts (which tend to be both flatter and wider, or large in diameter and length, e.g.: cylindrical). In addition, the present narrow bone allografts are more easily inserted into the patient through a (narrower) cannulated passageway.
In preferred aspects, two cannulae are used for positioning the pair of bone allografts, with the cannulae positioned at opposite posterolateral angles to one another. One cannula is used to position the first bone allograft and one cannula is used to position the second bone allograft. In this aspect, the angle between the bone allografts preferably corresponds to the angle between the cannulae. Accordingly, each of the bone allografts can be inserted directly into the patient""s intervertebral space in a relatively straight path through the cannula(e) and into the patient""s intervertebral space. As such, the present pair of bone allografts are easily positioned at a preferred angle to one another when initially deployed in a percutaneous posterolateral approach procedure. Moreover, in preferred aspects, the bone allografts can be inserted into the intervertebral space and then rotated by approximately 90xc2x0 to achieve vertebral distraction, tensioning the annulus and opening the foramen, thereby decompressing the nerve root.
As stated above, in a preferred aspect of the present invention, both the bone allografts and the facet screws are positioned in the patient""s spinal region through a posterolateral minimally invasive approach, which may optionally include a cannulated approach.
Prior to installing the present bone allografts and facet screws, a portion (or all) of the patient""s intervertebral disk may be removed (i.e.: a xe2x80x9cdiskectomyxe2x80x9d may be performed). Thereafter, the opposite vertebral endplates of the adjacent vertebrae may optionally be decorticated, which may produce a natural healing (bone fusion) response, if desired.
Thereafter, and in accordance with the present invention, the pair of bone allografts are positioned in the patient""s intervertebral space. Preferably the bone allografts are inserted through posterolaterally introduced cannulae. In preferred aspects, two cannulae are used, with one positioning each bone allograft; however, the use of a single cannula to place the two bone allografts one after another (in opposite posterolateral approaches) is also contemplated. Additionally, the two bone allografts could be placed through one cannula positioned from only one posterolateral direction. Advantageously, each of the pair of bone allografts can be positioned (i.e.: inserted into the intervertebral space) through a separate cannula with the posterolateral angle at which the cannulae are disposed corresponding to the angle between the bone allografts.
Preferably, after the bone allografts have been positioned between the adjacent vertebrae, the bone allografts will support the vertebrae, causing the vertebrae to move into a natural lordotic angle limiting facet joint movement such that it becomes easier to insert the facet screws.
The present facet screws are used to secure a patient""s facet joints together, thus preventing relative movement therebetween. An advantage of using facet screws is that they provide stabilization to the spine, but are not as surgically time consuming to install as, for example, pedicle screws. Another advantage of the present system is that, by immobilizing adjacent facet joints, it provides stability for vertebral arthrodesis between the adjacent vertebrae.
In accordance with the present invention, therefore, a system is provided to position a facet screw to secure a patient""s opposite adjacent first and second facet joints together, and to promote fusion therebetween. Each of the facet screws may preferably be positioned such that it passes through, and locks together, the superior articular process of one vertebrae with the inferior articular process of an adjacent vertebrae. Preferably, the threads of the facet screw extend all the way into the pedicle, thus providing increased anchoring strength. This embodiment is called the transfacet approach. Other approaches for facet screw placement are also contemplated (i.e. the translaminar approach) within the scope of the present invention.
Accordingly, each of the facet screws provides support at an opposite posterior (rear) side of the patient""s vertebral column. Together with the bone allografts, which provide support at the anterior (front center) of the vertebral column, the present system of two bone allografts and two facet screws, provides a xe2x80x9ctriangularxe2x80x9d support structure.
In an optional preferred aspect of the invention, autologous bone graft material is harvested from the patient and is delivered percutaneously into the patient at a location adjacent to the bone allografts. Specifically, the autologous bone graft material may be positioned both behind the allografts (i.e.: within the V-shape formed by the two allografts) and to the rear of the bone allografts (i.e.: behind the allografts in their posterolateral direction of approach). In preferred aspects, the autologous bone graft material may be harvested from the patient""s iliac crest. Such harvesting of bone graft material directly from the patient""s iliac crest is especially advantageous when the minimally invasive approach used passes through the patient""s iliac crest, with bone material being removed from the iliac crest to provide cannulated access to the patient""s intervertebral space.
In preferred aspects, the present bone allografts are dimensioned with a height of 0.20 to 0.75 inches, a width of 0.20 to 0.75 inches, and a length of 0.60 to 1.20 inches. In one particular preferred aspect, the present bone allografts are dimensioned with a height of about 0.40 inches, a width of about 0.25 inches, and a length of about 0.80 inches.
In preferred aspects, the height to width ratio of the allografts is about 1.2 to 2.0. In more preferred aspects, the height to width ratio of the allografts is about 1.4 to 1.8. In more preferred aspects, the height to width ratio of the allografts is about 1.6.
In preferred aspects, the bone allografts are positioned between adjacent vertebrae by an inserter. Optionally, a two pronged inserter may be used with each of the bone allografts held between the prongs of the inserter. In preferred aspects, the bone allografts may be formed with lateral gooves in which the prongs of the inserter are received.
In optional preferred aspects, the bone allografts may be formed with a curved front edge such that they can be positioned near the outer (front) perimeter of the intervertebral space, thereby advantageously resting on the hard cortical bone at the perimeter of the vertebrae. Most preferably, each of the bone allografts are formed such that their curved front end is the hardest portion of the bone allograft, thereby providing greatest support around the curved front end of the allograft.
In optional aspects, the positioning of the bone allografts may also involve distraction of the vertebrae, which may be performed by the inserter itself, by the shape of the bone allograft itself, or by additional tools (which may also be received through the cannula(e).
In accordance with the present invention, the two facet screws are also positioned in a percutaneous posterolateral approach (which may optionally be cannulated).
In preferred aspects, the cannulae (through which both the bone allografts and the facet screws are advanced) are positioned with the assistance of a surgical guideframe.